Synthesis, characterisation and molecular structure of Re(iii) 2-oxacyclocarbenes stabilised by a benzoyldiazenido ligand

Abstract

A family of new Fischer-type rhenium(III) benzoyldiazenido-2-oxacyclocarbenes of formula [(ReCl2[eta1-N2C(O)Ph][=C(CH2)nCH(R)O](PPh3)2][n = 2, R = H (2), R = Me (3); n = 3, R = H (4), R = Me (5)] have been prepared by reaction of [ReCl2[eta2-N2C(Ph)O](PPh3)2] (1) with omega-alkynols, such as 3-butyn-1-ol, 4-pentyn-1-ol, 4-pentyn-2-ol, 5-hexyn-2-ol in refluxing THF. The correct formulation of the carbene derivatives 2-5 has been unambiguously determined in solution by NMR analysis and confirmed for compounds 2-4 by X-ray diffraction methods in the solid state. All complexes are octahedral with the benzoyldiazenido ligand, Re[N2C(O)Ph], adopting a "single bent" conformation. The coordination basal plane is completed by an oxacyclocarbene ligand and two chlorine atoms. Two triphenylphosphines in trans positions with respect to each other complete the octahedral geometry around rhenium. The reactivity of 1 towards different alkynes and alkenes including propargyl- and allylamine has been also studied. With propargyl amine, monosubstituted or bisubstituted complexes, [(ReCl2[eta1-N2C(O)Ph][eta1-NH2CH2C triple bond CH]n(PPh3)(3-n)][n= 1 (6); n = 2 (7)], have been isolated depending on the reaction conditions. In contrast, the reaction with allylamine gave only the disubstituted complex [(ReCl2[eta1-N2C(O)Ph][eta1-NH2CH2CH=CH2]2(PPh3)] (8). The molecular structure of the monosubstituted adduct has been confirmed by X-ray analysis in the solid state.

Crystal structure of tert-butyl 4-[4-(4-fluorophenyl)-2-methylbut-3-yn-2-yl]piperazine-1-carboxylate

“…The bond length between C1-C6 [1.351 (4) Å ] is the shortest among all the bond lengths in the phenyl group, possibly due to the inductive effect of fluorine. The spatial distance between the extreme atoms of propargylamine groups (C7Á Á ÁN1) was observed to be 3.508 (3) Å , which is slightly longer than for the other reported propargylamines (3.372-3.478 Å ; Marvelli et al, 2004;Sidorov et al, 1999Sidorov et al, , 2000, and possibly due to the open L-shaped structure of the molecule. Also, the piperazine ring is shown in its most stable chair form conformation in Fig.…”

Mechanisms and Beyond: Elucidation of Fluxional Dynamics by Exchange NMR Spectroscopy

“…In many “push–pull” alkenes, however, the interconversion barrier can be significantly lowered. Similarly, low barriers were observed for N=N bond rotation in Re complexes 121 a / b (Scheme ) …”

“…Similarly, low barriers were observed for N=Nb ond rotation in Re complexes 121 a/b (Scheme 38). [193] Bain and co-workers showed that in the crotonate 122 [194] rotation aboutt he nominally double bond has only 11-12 kcal mol À1 barrier whereas degenerate rotation of Me 2 NinE-122 requires 12-16 kcal mol À1 owing to entropye ffects and dipole moments of the ground and transition states. Ad ifferent dissociative mechanism of spontaneous Z/E interconversion of nitrosopyridine 123 was observed by Orrell's group.…”

Organometallic rhenium(iii) chalcogenide clusters: coordination of N-heterocyclic carbenes

“…Even Re(III) Fischer carbenes are rare; however, the one report we found characterized four Re(III)-Fischer carbene complexes with bond distances ranging from 1.990-2.021 Å. 15 In 1 2+ , the rhenium-carbene bond distance (Re6-C1) is 2.248 (16) Å. This longer bond length indicates a weaker interaction with the metal center.…”